Dual-element centrifugal pump pressure responsive flow regulator means

ABSTRACT

A pumping system utilizing at least one high flow capacity impeller and one low flow capacity impeller to meet the flow delivery requirements of a widely variable flow range. A control means for selecting only the low flow capacity impeller for low flow requirements and, at greater flow demands, operate to concurrently activate the high flow capacity impeller and divert the flow of the low flow impeller through the high flow impeller in a series relationship.

United States Patent Jackson 15] 3,658,440 51 Apr. 25, 1972 [54] DUAL-ELEMENT CENTRIFUGAL PUMP PRESSURE RESPONSIVE FLOW REGULATOR MEANS,

[72] Inventor: Clive G. B. Jackson, Clayville, N.Y.

[ 73] Assignee: The Bendix Corporation [22] Filed: Jan. 28, 1970 [21] App1.No.: 6,626

[52] US. Cl ..417/62 [51] Int. Cl ..F04b 23/04 [58] Field of Search ..417/62, 423; 415/143, 144, 415/145, 101

[56] References Cited UNITED STATES PATENTS 2,218,565 10/1940 Vickers ..417/62 Primary Examiner-Robert M. Walker AnomeyWilliam S. Thompson and Bruce A. Yungman [57] ABSTRACT A pumping system utilizing at least one high flow capacity impeller and one low flow capacity impeller to meet the flow delivery requirements ofa widely variable flow range. A control means for selecting only the low flow capacity impeller for low flow requirements and, at greater flow demands, operate to concurrently activate the high flow capacity impeller and divert the flow of the low flow impeller through the high flow impeller in a series relationship.

9 Claims, 2 Drawing Figures PATENTEDA R 25 I912 3, 658 440 SHEET 10? 2 CLIVE G. B. JACKSO'N INVENTOR.

PATENTEDAPR 25 I972 I 3, 658,440

sum 2 CF 2 FlGURE 2 CLIVE a. B. JACKSON INVENTOR.

DUAL-ELEMENT CENTRIFUGAL'PUMP PRESSURE I RESPONSIVE FLOW REGULATOR MEANS FIELDOF THE INVENTION DESCRIPTION OF THE PRIOR ART In aircraft gas turbine fuel pumping systems, especially for thrust augmentor or afterbumer fuel supply, it is often required that the fuel pump operate over a very wide flow range. Considerations of weight, size and insensitivity to contaminants in the pumped fluid usually result in the choice of a high speed centrifugal pump for such a duty. It is practically impossible to utilize a single element, i.e., one impeller, high speed centrifugal pump over a wide low range without generating excessive heat due to the internal hydraulic losses in such a pump. Since there is a temperature limitation placed on the heat of the fuel, the use of a dual-element pump is often dictated.

In the dual-element pump there are two ccentrifugal impellers, usually, but not necessarily, mounted coaxially on a common drive shaft. One impeller operates in the lower end of the flow range and the other operates in the upper end of the flow range. Valving means, actuated by hydraulic signals from an external control unit, are provided for the purposes of selecting one or the other of the pumping elements as required, and for venting one or both of the elements when to required; it is common for augmentor pumps to spend 95 percent of their operational life running .dry. It is important to empty the pumping elements when they are inoperative, i.e., no flow demand, because the pump is directly driven from the engine and, in the event an inoperative element remains full of fuel, the rapid generation of heat could cause seizure of the pump bearings in a few seconds.

In addition to the above, the valving means taught by the prior art areusually provided with interlocks so that the following conditions may be met:

a. the high capacity impeller can only be activated if the low capacity impeller is already pumping;

b. the low capacity impeller cannot cease pumping until the high capacity impeller is generating a pressure equal to that of the low capacity impeller;

c. the low capacity impeller must cease pumping when the high capacity impeller is established irrespective of the status of the control signals; and I d. when switching from the high capacity impeller to the low capacity impeller, the high capacity element cannot cease pumping until the low capacity impeller is established.

These stringent requirements as to the sequence of operations are difficult to achieve in practice and the valving means become unacceptably complex and sensitive to contaminants I in the fuel. It is the purpose of this disclosure to descirbe a means of operating a dual-element centrifugal pump in a manner not previously attempted and permitting the control means to be made simpler, lighter, and less sensitive to contaminants thus providing a more efficient fuel pumping system.

The proposed mode of operation avoids the necessity for interlocks because the low capacity impeller remains in operation when the high capacity impeller is pumping. A secondary but important advantage is that the suction specific speed requirement of the high capacity impeller is reduced since a proportion of the total pump output is contributed by the low capacity impeller throughout the flow range.

SUMMARY OF THE INVENTION The present invention comprises a dual-element centrifugal pumping apparatus wherein a flow regulator means communicates the two impellers such that the low capacity impeller feeds the high capacity impeller in series during high demand periods. A means is provided for controlling the rate of flow through said flow regulator means. Further, the flow regulator means is constructed so as to prevent backflow from the high capacity impeller, should the low capacity impeller be inadvertently rendered inoperative during high demand periods. Vent valves are used for draining the impeller housings when the pumping elements are required to be emptied of fuel thus preventing seizure of the pump bearings during dry operation.

The mode of operation disclosed by this pumping apparatus avoids the necessity for a plurality of sequencing interlocks since the low capacity impeller remains in operation over the entire flow range.

The above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side view of the preferred embodiment of the invention.

FIG. 2 is a diagrammatic side view of an alternative embodiment of the invention which combines the valving means of the larger capacity impeller with the flow regulator means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, an inlet conduit 10 is shown connected to fluid conveying passages 12 and 14. Passages l2 and 14 form the inlets and outlets for the shut-off valves 16 and 18 respectively. Shut-off valves 16 and 18 control the admission of fluid to the pumping elements denoted generally as l and 2 respectively.

Shut-off valves 16 and 18 are diagrammed as piston operated poppet valves, but any suitable type of on-off" valve may be used, or in some cases a valve having shaped ports or tapered pistons may be used to prevent pressure surging thus allowing the valves to open gradually. Valves 16 and 18 are fastened by piston rods 20 and 22 to pistons 24 and 26 respectively. The pistons 24 and 26 move axially in cylinders 28 and 30 under the influence of compression springs 32 and 34 respectively, and the applied hydraulic signals 3 and 4 respectively. Pistons 24 and 26 divide cylinders 28 and 30 under the influence of compression springs 32 and 34 respectively, and the applied hydraulic signals 3 and 4 respectively. Pistons 24 and 26 divide cylinders 28 and 30 into four chambers, i.e., two per cylinder. The two chambers of cylinders 28 and 30 that house the springs 32 and 34 are connected by pipes 36 and 38 to passages 12 and 14 respectively. The rod end faces of pistons 24 and 26 and the cylinders 28 and 30 define chambers 48 and 50 respectively. Passages l2 and 14 contain orifices 40 and 42 which receive piston rods 20 and 22 respectively.

Chambers 48 and 50 receive hydraulic signals 3 and 4 which signal pressure is additionally transmitted to vent valve housings 56 and 58 through pipes 52 and 54 respectively.

CThe venting valves are diagrammed as ball valves although other suitable valves may be used. Vent valve housings 56 and 58 incase respectively a) pistons 60 and 62 which pistons are fastened to piston rods 64 and 66 respectively, b) helical compression springs 68 and 70, and c) ball valves 72 and 74. Springs 68 and 70 engage the projecting walls of housings 56 and 58 with the rod side of pistons 60 and 62 respectively; piston rods 64 and 66 move axially within the compression springs 68 and 70. The large area faces of pistons 60 and 62 and the valve housings 56 and 58 define chambers 76 and 78, which chambers are connected to pipes 52 and 54 respectively. The ends of valve housings 56 and 58 that contain ball valves 72 and 74 form valve seats and 82 respectively. Housings 56 and 58 also connect to atmospheric vent passages 84 and 86 and the impeller housing venting passages 88 and 90 respectively.

The centrifugal vane type impellers 6 and 7 are mounted coaxially on a common drive shaft 11. Impeller 6 has heretofore been referred to as the low capacity impeller, and impeller 7 has been referred to as the high capacity impeller. Although impeller 7 is somewhat larger than impeller 6 in the preferred and alternative embodiments, one learned in the art should recognize the possibility of utilizing equally sized impellers to obtain the economic benefits inherent in manufacturing common parts and instead provide a gear reduction between the impellers to vary their respective speeds.

impellers 6 and 7 are provided with axial flow inducers l3 and respectively which inducers are also mounted coaxially on drive shaft 11. (Pump inlet pressure may also be boosted by an external backing pump instead of using flow inducers.) 1mpellers 6 and 7 are incased in housings 8 and 9 respectively.

The small impeller housing 8 is connected by discharge channel 17 to a spring biased-closed discharge check valve 19. The impeller housing 8 has an orifice at the point where venting passage 88 is connected. The large impeller housing 9 is connected by discharge channel 21 to a spring biased-closed check valve 23. Discharge check valve 23 is connected by intermediate discharge channel 25 to discharge check valve 19. Fuel is pumped through channels 17, 25, and 21 to a common discharge conduit 5.

Impeller housings 8 and 9 are connected to the flow regulator housing 31 by passages 27 and 29 respectively. Passage 27 connects to impeller housing 8 at its periphery and to the flow regulator housing 31 at its inlet orifice 33. (Passage 27 could also be connected to passage 17 just upstream of check valve 19). The regulator housing 31 and the flow regulator valve 35 define a channel 37. Passage 29 connects the channel 37 to an annulus 39 in the large impeller housing 9. The regulator housing 31 forms a valve seat 41 for the regulator valve 35. The regulator valve 35 is hollow and cylindrical with an open end. The hollow section of regulator valve 35 receives in antibackflow compression spring 43; this cavity also receives piston rod 51. The compression strength of spring 43 is such that it will allow regulator valve 35 to open whenever impellers 6 and 7 are both in operation and when regulator valve 35 is not under the influence of piston rod 51, but also of such a strength that it will force regulator valve 35 to its closed position whenever impeller 6 ceases to operate regardless of the pumping status ofimpeller 7.

Passage 29 is connected radially inward of impeller 7 at an annulus 39 in impeller housing 9. the annulus 39 is located so that the centrifugal pressure at annulus 39 is less than the centrifugal pressure at the delivery of the low capacity impeller 6 when both impellers 6 and 7 are pumping. The size of annulus 39 and the rate of flow of fluid from impeller 6 to impeller 7 is directly related. As the pressure differential between the delivery at impeller 6 and the centrifugal pressure at annulus 39 is increased, the rate of flow between the impellers is also increased, and said pressure differential is increased by decreasing the radius of the annulus 39; i.e., the centrifugal pressure at annulus 39 decreases as the radius of annulus 39 decreases. This relationship holds true when both high and low capacity impellers are driven at the same speed and the impeller capacity variance is achieve solely by utilizing different sized impellers. If some gear reduction or other pump structural change exists between impellers 6 and 7 so that they are driven at different speeds, or have different sizes and varying efficiencies, it will be understood the above relationship would be altered so as to conform to these differences.

Flow regulator valve 35 is held firmly closed by piston rod 51 whenever impeller 7 is inoperative i.e., not pumping). The operation of piston rod 51 is controlled by a spring biasedclosed piston 53 which is housed in cylinder 55. Piston 53 divides cylinder 55 into two chambers 57 and 61. Compression spring 59 is contained in chamber 57 and engages the bottom of cylinder 55 and the large area face of piston 53. Fluid is allowed to enter and exit chamber 57 through pipe 65 which connects cylinder 55 to passage 12. Hydraulic signal 4 is transmitted to chamber 61 by a passage 63 that connects cylinder 55 to pipe 54.

OPERATION OF THE PREFERRED EMBODIMENT Shaft 11 is driven by the jet engine; since impellers 6 and 7 are mounted to shaft 11 said impellers are for the great majority of the time windmilling" i.e., shaft 11 continually rotates so long as the engine driving it is running.

Fluid enters the pump through inlet conduit 10 and is transferred to the pumping elements 1 and 2 through passages 12 and 14 respectively. Assuming that there are no hydraulic signals present in the system, shut-off valves 16 and 18 will be seated in their respective valve seats 44 and 46. in this position compression springs 32 and 34 act against the pistons 24 and 26, respectively, forcing said pistons closed thus seating the valves. Additionally, in the absence of a hydraulic control signal, the compression springs 68 and 70 of the vent valves act against the pistons 60 and 62 opening their respective ballvalves 72 and 74, thus emptying impeller housings 8 and 9 through passages 88 and 90 respectively. When the fluid reaches the ball valves, it is transferred through passages 84 and 86 to some dump reservoir (not shown) which may be vented directly to the atmosphere.

Assume now that low flow is required. A hydraulic signal 3 is transmitted to chamber 48 within cylinder 28. Pressure is exerted on the annular piston rod side of piston 24 forcing said piston and shut-off valve 16 open against the bias force of spring 32; fluid is thereby admitted to pumping element 1. Fluid contained in the spring-side chamber of cylinder 28 is allowed to be vented through passage 36 to passage 12. The same hydraulic signal is transmitted through pipe 52 to chamber 76 in vent valve housing 56. Pressure is exerted on the large area face of piston 60 thus compressing spring 68. As piston 60 moves axially within valve housing 56. the piston rod 64 forces the ball valve 72 against its seat 80 thus preventing fluid from being drained from the impeller housing 8.

The fluid is directed at impeller 6 by axial flow inducer 13. (Although axial flow inducers 13 and 15 are not mandatory, they do assist in obtaining the desired suction performance.) impeller 6 generates pressure and opens the spring biasedclosed discharge check valve 19. The fluid is pumped through discharge channel 17, then through intermediate discharge channel 25 to the common discharge conduit 5. The centrifugal pressure generated by impeller 6 is also communicated through passage 27 to the flow regulator valve 35 at orifice 33 in the flow regulator housing 31. However, regulator valve 35 remains closed against its seat 41 because of the load exerted by spring 59 on piston 53 transmitted by piston rod 51 which bears against the back side of regulator valve 35.

When a higher flow is demanded requiring the activation of pumping element 2, hydraulic signal 4 is transmitted to chamber 50 within cylinder 30. Pressure is exerted on the annular piston rod side of piston 26 forcing said piston and shutoff valve 18 open against the bias force of spring 34; fluid is thereby admitted to pumping element 2. Fluid contained in the spring-side chamber of cylinder 30 is allowed to be vented through passage 38 to passage 14. The same hydraulic signal is transmitted through pipe 54 to chamber 78 in vent valve housing 58. Pressure is exerted on the large area face of piston 62 thus compressing spring 70. As piston 62 moves axially within valve housing 58, piston rod 66 forces ball valve 74 against its seat 82 thus preventing fluid from being drained from impeller housing. The fluid is directed at impeller 7 by the use of axial flow inducer l5. Impeller 7 generates pressure and opens the spring biased-closed discharge check valve 23. The fluid is pumped through discharge channel 21 into common discharge conduit 5. Simultaneously, the hydraulic signal is transmitted through passage 63 to chamber 61 in cylinder 55. Pressure is exerted on the annular piston rod side of piston 53 removing the load applied by spring 59 on regulator valve 35, thus allowing said valve to open. The fluid contained in chamber 57 of the cylinder 55 is forced out of the cylinder by piston 53; pipe 65 allows this fluid to be received into passage 12.

Since impeller 7 is larger than impeller 6 and since both impellers are rotating at the same speed, in the illustrated case, impeller 7 generates a higher pressure than impeller 6; this difference in pressure at the outlet of the two impellers causes spring biased discharge check valve 19 to close. Pumping element 1 is still activated, however, and its output is now diverted through passage 27, channel 37, and then through passage 29 to annulus 39 in impeller housing 9. In the specific case shown, annulus 39 has an outside diameter somewhat smaller than the diameter of impeller 6; therefore, since bothimpellers 6 and 7 are rotating at the same speed, the centrifugal pressure at the annulus 39 is less than that at the periphery of impeller 6 and it is the difference between these two pressures and the losses through the interconnecting means that determines the rate of flow of fluid between said impellers. Assuming the speed remains substantially constant, impeller 6 will discharge a constant flow to impeller 7.

Should the hydraulic signal in channel 3 be inadvertently removed or lost while impeller 6 is delivering fluid to impeller 7, impeller 6 will be shut down by the closing of valve 16 and impeller housing 8 will be vented in the normal manner. Back flow from impeller 7 through regulator housing 31 is prevented by the closing of regulator valve 35 under the influence of its own spring 43. The proportion of the pump output which was provided by impeller 6 is then made up through inlet passage 14 under normal fuel boost pressure conditions.

DESCRIPTION AND OPERATION OF ALTERNATIVE EMBODIMENT Referring to FIG. 2, this embodiment of the invention replaces regulator valve 35 and the piston-cylinder assembly that operated valve 35 with a double acting regulator valve 75; valve 75 is actuated by the movement of piston 26.

Piston rod 22 is extended beyond piston 26 and passes through a seal 73 at the end of cylinder 30. Regulator valve 75 is slidably mounted on the piston rod 22 such that, with the shut-off valve 18 in its fully closed position, regulator valve 75 is seated by spring 77. Therefore when only pumping element I is pumping, fluid is prevented from passing from impeller housing 8 to impeller housing 9 through the interconnecting passage 71.

When-pumping element 2 is activated by signal 4 and valve 18 begins to open, regulator valve 75 remains closed until a shoulder 81 mounted on rod 22 abuts the right end of regulator valve 75; further movement of piston rod 22 opens regula tor valve 75 thus permitting fluid to be pumped through passage 71 to an orifice 83 in impeller housing 9. The lost movement" is provided so that the large impeller housing 9 may fill and impeller 7 may raise pressure before the output of impeller 6 is diverted through passage 71. Orifice 83 is impeller housing 9 is placed so that the centrifugal pressure at orifice 83 is somewhat less than the pressure at the periphery of impeller 6; this difference in pressure determines the rate of flow through channel 71.

If at any time hydraulic signal 3 is lost while impeller 7 is pumping, i.e., pumping element 1 shuts down and pumping element 2 continues to pump, regulator valve 75 will act in the reverse sense as a check valve under the influence of spring 77 to prevent fluid passing from impeller 7 to impeller housing 8.

The other features of the invention are set out in the description of the operation of the preferred embodiment and should be read in conjunction with the above. Parts of the embodiment not specifically labeled in FIG. 2 are the same as the identical parts labeled in FIG. 1.

lclaim:

I. A pump comprising in combination fluid intake means including at least one inlet conduit;

first impeller means which operates over the entire output range;

second impeller means which operates during high output periods;

shaft means for connecting said impeller means to a source of rotary power;

flow regulator means for intercommunicating said first and second impeller means so that said impeller means pump is series during high output periods;

means for (acontrolling the admission of fluid to said second impeller means, said control means being in communication with said flow regulator means such that said control means activates said flow regulator means; and

means for receiving the discharged fluid from either of the impeller means.

2. A pump comprising in combination an inlet conduit;

first impeller means which operates over the entire output range;

second impeller means which operates during high output periods;

shaft means for connecting said impeller means to a source of rotary power;

venting means for communicating said second impeller means to atmosphere during dry operation;

valving means for controlling the admission of fluid to said second impeller means; said valving means also controlling the venting means for said second impeller means;

flow regulator means for intercommunicating said first and second impeller means, said flow regulator means including a plurality of passages interconnecting said first and second impellers means and a biased-closed regulator valve interposed within said passages and in communication with said valving means, so that when a higher flow output is required, said regulator valve opens thus permitting said first impeller means to deliver its output to said second impeller means through said interconnecting passages; and

fluid receiving means for communicating the discharged fluid fromeither of the impellers to a common discharge conduit.

3. A pump as recited in claim 2 in which the regulator valve is biased closed under the influence of a piston rod, said piston rod being part of an adjacent but separate piston-cylinder assembly.

4. A pump as recited in claim 3 in which the regulator valve encases a compression spring, said spring being of a predetermined strength so that said regulator valve will open when not under the influence of said piston-cylinder assembly and so that said regulator valve will close independently of said piston assembly should the first impeller means stop pumping while the second impeller means remains in operation.

5. A pump as recited in claim 2 in which the regulator valve is biased closed by a compression spring positioned within said plurality of passages on the upstream side of said regulator valve.

6. A pump as recited in claim 2 including the following additional elements:

means for controlling the rate of fluid through said intereconnecting passages, said means comprising in combination a housing encasing said second impeller means, said housing containing an annulus therein, said annulus being located in said housing in an area where the pressure is less than the pressure at said first impeller means periphery when both first and second impeller means are in pumping operation, so that this pressure differential determines the rate of flow of fluid passing through said passages connecting said first impeller means to said second impeller means.

7. A pump as recited in claim 2 including the following additional elements:

means for controlling the rate of flow of fluid through said interconnecting passages, said means comprising in combination a housing encasing said second impeller means, said housing containing an orifice therein, said orifice being located at a point in said housing where the pressure is less than the pressure at said first impeller means periphery when said first and second impeller means are in pumping operation, so that this pressure differential between said orifice and said first impeller means periphery determines the rate of flow of fluid passing through the passageways connecting the first impeller means to the second impeller means.

8. A pump comprising in combination an inlet conduit;

a first impeller which operates over the entire output range;

a second impeller which operates during high output periods;

shaft means for connecting said impellers to a source of rotary power;

venting means for communicating said second impeller to atmosphere during dry operation;

flow regulator means for intercommunicating said first and second impellers so that said impellers pump in series during high output periods, said regulator means comprising a plurality of passages interconnecting said first and second impellers and a biased-closed regulator valve interposed within said passages;

means for controlling the rate of flow of fluid through said interconnecting passages, said means including housing means encasing said second impeller, said housing means containing an annulus therein, said annulus being located in said second impellers housing at an area where the pressure is less than the pressure at said first impellers periphery when both first and second impellers are in pumping operation, so that this pressure differential determines the rate of flow of fluid passing through said passages connecting said first impeller to said second impeller;

valving means for controlling the admission of fluid to said second impeller, said flow regulator means, and said venting means for said second impeller said valving means being actuated by a hydraulic signal from an external fluid control unit; and

fluid receiving means for communicating the discharged fluid from either of the impellers to a common discharge conduit; said discharge conduit having a first and second check valve interposed therein, said first valve being associated with said first impeller, said second valve associated with said second impeller so that said first valve opens during low output periods, and said first valve closes and said second valve opens during high output periods,

9. A pump comprising in combination an inlet conduit;

a first impeller which operates over the entire output range;

a second impeller which operates during high output periods;

shaft means for connecting said impeller to a source of rotary power;

venting means for communicating said second impeller to atmosphere during dry operation;

flow regulator means for intercommunicating said first and second impellers so that said impellers pump in series during high output periods, said regulator means comprising a plurality of passages interconnecting said first and second impellers and a biased-closed regulator valve interposed within said passages; and

means for controlling the rate of flow of fluid through said interconnecting passages, said means including housing means encasing said second impeller, said second impeller housing means containing an orifice therein. said orifice being located at a point in said second impeller's housing where the pressure is less than the pressure at said first impellers periphery when both first and second impellers are in pumping operation, so that this pressure differential between said orifice and said first impellers periphery determine the rate of flow of fluid passing through the passageways connecting the first impeller to the second impeller.

UNITED STATES PATENT OFFIC E CERTIFICATE OF CORRECTION Patent No. ,658,440 Dated May 8, I972 Inventor) Clive G. B. Jackson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE DESCRIPTION OF THE PRIOR ART l, Line 19: "low" should read ---fl'ow--- Column 1, Line 24: "ccentrifugal" should read ---centrifugal-- Column l, Line 31: "to" should read ---not--- Column l, Line 56: "descirbe" should read ---describe--- IN THE DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Column 2, Line 44 Omit the following: Pistons 24 and 26 divide cylinders 28 and 30 Column 2, Line 45 ('3) Omit the following: under the influence of compression springs 32 and 34 respec- Column 2, Line 46 ('2) Omit the following: tively and the applied hydraulic signals 3 and 4 respectively.

' Column 2, Line 60 "CThe" should read --The--- Column 3, Line 35: "in" should read ---an--- Column 3, Line 59: "achieve" should read ---achieved--- -IN THE OPERATION OF THE PREFERRED EMBODIMENT Column 4, Line 62: After the word "housing" add ---9--- IN THE DESCRIPTION AND OPERATION OF ALTERNATIVE EMBODIMENT Column 5, Line 49: "is" should read ---in--- IN THE CLAIMS Column 5, Line 75: "is" should read ---in Column 6 Line l "(acontrol l ing" should read --control 1 ing-- Column 6 Line 50: After "of" add --flow of--- Signed and sealed this 5th day' of September 1972.

(SEAL) Attest:

T M.I LETCI-IER ,JR. ROBERT OOTTSCHALK Officer Commlssloner of Patents 

1. A pump comprising in combination fluid intake means including at least one inlet conduit; first impeller means which operates over the entire output range; second impeller means which operates during high output periods; shaft means for connecting said impeller means to a source of rotary power; flow regulator means for intercommunicating said first and second impeller means so that said impeller means pump is series during high output periods; means for (acontrolling the admission of fluid to said second impeller means, said control means being in communication with said flow regulator means such that said control means activates said flow regulator means; and means for receiving the discharged fluid from either of the impeller means.
 2. A pump comprising in combination an inlet conduit; first impeller means which operates over the entire output range; second impeller means which operates during high output periods; shaft means for connecting said impeller means to a source of rotary power; venting means for communicating said second impeller means to atmosphere during dry operation; valving means for controlling the admission of fluid to said second impeller means; said valving means also controlling the venting means for said second impeller means; flow regulator means for intercommunicating said first and second impeller means, said flow regulator means including a plurality of passages interconnecting said first and second impellers means and a biased-closed regulator valve interposed within said passages and in communication with said valving means, so that when a higher flow output is required, said regulator valve opens thus permitting said first impeller means to deliver its output to said second impeller means through said interconnecting passages; and fluid receiving means for communicating the discharged fluid from either of the impellers to a common discharge conduit.
 3. A pump as recited in claim 2 in which the regulator valve is biased closed under the influence of a piston rod, said piston rod being part of an adjacent but separate piston-cylinder assembly.
 4. A pump as recited in claim 3 in which the regulator valve encases a compression spring, said spring being of a predetermined strength so that said regulator valve will open when not under the influence of said piston-cylinder assembly and so that said regulator valve will close independently of said piston assembly should the first impeller means stop pumping while the second impeller means remains in operation.
 5. A pump as recited in claim 2 in which the regulator valve is biased closed by a compression spring positioned within said plurality of passages on the upstream side of said regulator valve.
 6. A pump as recited in claim 2 including the following additional elements: means for controlling the rate of fluid through said intereconnecting passages, said means comprising in combination a housing encasing said second impeller meanS, said housing containing an annulus therein, said annulus being located in said housing in an area where the pressure is less than the pressure at said first impeller means periphery when both first and second impeller means are in pumping operation, so that this pressure differential determines the rate of flow of fluid passing through said passages connecting said first impeller means to said second impeller means.
 7. A pump as recited in claim 2 including the following additional elements: means for controlling the rate of flow of fluid through said interconnecting passages, said means comprising in combination a housing encasing said second impeller means, said housing containing an orifice therein, said orifice being located at a point in said housing where the pressure is less than the pressure at said first impeller means periphery when said first and second impeller means are in pumping operation, so that this pressure differential between said orifice and said first impeller means periphery determines the rate of flow of fluid passing through the passageways connecting the first impeller means to the second impeller means.
 8. A pump comprising in combination an inlet conduit; a first impeller which operates over the entire output range; a second impeller which operates during high output periods; shaft means for connecting said impellers to a source of rotary power; venting means for communicating said second impeller to atmosphere during dry operation; flow regulator means for intercommunicating said first and second impellers so that said impellers pump in series during high output periods, said regulator means comprising a plurality of passages interconnecting said first and second impellers and a biased-closed regulator valve interposed within said passages; means for controlling the rate of flow of fluid through said interconnecting passages, said means including housing means encasing said second impeller, said housing means containing an annulus therein, said annulus being located in said second impeller''s housing at an area where the pressure is less than the pressure at said first impeller''s periphery when both first and second impellers are in pumping operation, so that this pressure differential determines the rate of flow of fluid passing through said passages connecting said first impeller to said second impeller; valving means for controlling the admission of fluid to said second impeller, said flow regulator means, and said venting means for said second impeller said valving means being actuated by a hydraulic signal from an external fluid control unit; and fluid receiving means for communicating the discharged fluid from either of the impellers to a common discharge conduit; said discharge conduit having a first and second check valve interposed therein, said first valve being associated with said first impeller, said second valve associated with said second impeller so that said first valve opens during low output periods, and said first valve closes and said second valve opens during high output periods.
 9. A pump comprising in combination an inlet conduit; a first impeller which operates over the entire output range; a second impeller which operates during high output periods; shaft means for connecting said impeller to a source of rotary power; venting means for communicating said second impeller to atmosphere during dry operation; flow regulator means for intercommunicating said first and second impellers so that said impellers pump in series during high output periods, said regulator means comprising a plurality of passages interconnecting said first and second impellers and a biased-closed regulator valve interposed within said passages; and means for controlling the rate of flow of fluid through said interconnecting passages, said means including housing means encasing said second impeller, said second impeller housing means containing an orifice therein, said Orifice being located at a point in said second impeller''s housing where the pressure is less than the pressure at said first impeller''s periphery when both first and second impellers are in pumping operation, so that this pressure differential between said orifice and said first impeller''s periphery determine the rate of flow of fluid passing through the passageways connecting the first impeller to the second impeller. 